1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Horizontal spring, mass and nonconstant friction

  1. Apr 15, 2012 #1
    1. The problem statement, all variables and given/known data
    Hello! The problem is about spring with block attached to it. ( with spring constant = k) The system is on surface that has a friction μ increasing towards the direction of the blocks movement.

    Block is pushed -0,1m ( to the left ) from the equilubrium position and then released. The block moves from the starting position, +0,3m to the right ( +0,2m from the equilubrium position) and stops. What is the spring constant k?

    2. Relevant equations

    Spring constant = k
    Friction μ = 0,025 * x, increasing towards to the right.
    Mass of the block = 2,7 kg

    3. The attempt at a solution

    The most problematic part for me is the friction not being constant.

    I assume;

    From -0,1 m to 0,0 m the Force due to the spring and Force due to the friction are in different directions.

    From 0,0 m to 0,2 m the Force due to the spring and Force due to the friction are in same direction.

    I'm not sure, but as the accelereation ain't constant ( due to the both forces depending on some variable) should I be using some definite integrals?

    Or should I use some energy-theorem involving kinetic-energy and potential-energy?

    Sincerely yours,

    P.S I can draw a picture about the situation and scan it here, if the explanation ain't good enough. English isn't my native language. :)
  2. jcsd
  3. Apr 15, 2012 #2


    User Avatar
    Science Advisor
    Homework Helper

    Hi Siune! :smile:
    yes, use the work energy theorem (and a bit of integration) …

    (KE + PE)initial - (KE + PE)final = work done by friction :wink:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook